Cracking open the Osborne 1: The original portable computer

A classic luggable PC

The Osborne 1 was the word's first self-contained portable personal computer. Many of the design decisions and innovations first seen in the Osborne 1 are still being used today some 25-plus years later. We could not resist taking a look inside this piece of computing history in this TechRepublic Cracking Open Photo Gallery.

A quick note on the Cracking Open Photo Galleries: I am not an engineer and these galleries are not attempts to name every chip we see. So please, if you have knowledge about what is inside the Osborne 1, share it with us.

Keyboard

Remove a couple of screws at the underside of the keyboard is revealed.

Mechanical

The keyboard is a throwback to the era of typewriters.

Ribbon cable

Here we seen the common ribbon cable connecting the keyboard to the rest of the machine. I wonder if this was innovative or imitative? When were ribbon cables first used in these sorts of devices?

Spring

A better look

The familiar latch

The keyboard connects to the Osborne 1 using a ribbon cable and latch system.

Open the latch

Easily removed

The keyboard can be easily removed and then reattached.

Plastic

Our Osborne 1 has seen some time in a basement, attic, or some other place were the plastic could lose some of its strength. Notice that some of the screw holes have deprecated to the point where they don't actually hold the cover to the case anymore.

Nothing last forever

From this angle you can see where the some of the screw holes have disintegrated.

Getting inside

Apparently our Osborne 1 has been cracked open before -- there are several screws missing and later on I discover screws that just don't belong.

Warning

One thing I did notice as I worked my way through the case is that there a numerous warnings. Is opening a PC really all that dangerous?

Mostly floppy drive

With the case removed the most dominate parts seem to be the floppy drives.

A cathode ray tube

Our first look at the cathode ray tube for our display. This is by far the heaviest part in the Osborne 1.

Backside

Those ribbon cables connecting the two floppy drives to the controller look very familiar.

Power

The power assemblage looks impressive, we'll have to get a closer look.

Motherboard

The main circuit board is attached with three screws. Two look to be the original screws one is a flat-head replacement and one is just plain missing.

More to come

The remaining circuit board is associated with the power system. I have no idea what those scratches on the plastic frame is all about.

Chips ahoy!

Our Osborne 1 doesn't skimp when it comes to the overall number of chips.

Previous incursion explained

Apparently our Osborne 1 was upgraded with the double density floppy disk drive controller daughter board. I cannot explain why several screws went missing during that upgrade or subsequent maintenance.

The other end

The CPU can be found on this end of the board. The Osborne 1 used the Zilog Z80 processor running at 4MHz. Or at least a processor based on the Z80.

Memory banks

64K RAM takes up more room then you might think in 1981.

Hello Moto

These memory chips were provided by Motorola.

Except for that chip in the upper left corner. Perhaps this Osborne 1 was opened more than once.

International

Even in 1981, PC making was an international effort. You can see stamps from the Philippines, El Salvador, and Brazil.

Call to experts

Okay all you engineers out there -- what are the two chips from the Philippines for?

NEC

This Osborne 1 has the NEC version of the Z80 processor.

Fujitsu

The large chip above the unknown one from the Philippines is from Fujitsu. According to the chip's data sheet it is a Floppy Disk Formatter / Controller. That makes sense because of the floppy disk connection right next to the chip.

ROM

Which ROM is this?

Printer connection

Name plate

Details

Here are some more details about the origin of our Osborne 1.

You are my density

A close up look at the double-density controller board.

Power regulation

There certainly are a lot of capacitors.

Danger!

I guess it is dangerous - I was careful.

No leaks

Over 25 years old and no leaks -- take that Dell.

Fuse

The Osborne 1 uses an old fashioned fuse. I wonder if this had to be replaced before?

More warnings

The folks at Osborne really wanted to keep people away from this circuit board.

CRT

A close up look at the CRT. And more warnings about electricity.

CRT

CRT

More international flavor

The CRT, at least in part, seems to be from our friends at the Nippon Electric Company in Japan.

3M

Get the parts where you get the parts.

CRT

CRT

Floppy disk drive

The floppy drives are called full-sized but this is ridiculous. This drive is almost the size of a modern notebook computer.

Belt driven

The drive mechanism is belt driven -- seems to be asking for failure.

Floppy chips

It took quite a bit of computing power to read and write files to a floppy disk in 1981, if the number of chips involved can be used as a measure.

Texas Instruments

Looks like Motorola and Texas Instruments were the prominent players for this chip set.

Look at all that space

No wonder later iterations of the floppy drive were cut in half -- most of this drive is wasted empty space.

Another country

More international evidence -- Malaysia is represented.

Floppy drive

Engineer help needed

Okay, I need some help here. Is that part with the "wings" a heat sink?

Floppy drive

All the parts

The end

There were a surprisingly large number of parts in the Osborne 1. I will be interesting to see if the TRS-80 Model 4P has as many.

More warnings

The folks at Osborne really wanted to keep people away from this circuit board.

About Mark Kaelin

Mark W. Kaelin has been writing and editing stories about the IT industry, gadgets, finance, accounting, and tech-life for more than 25 years. Most recently, he has been a regular contributor to BreakingModern.com, aNewDomain.net, and TechRepublic.

Full Bio

Mark W. Kaelin has been writing and editing stories about the IT industry, gadgets, finance, accounting, and tech-life for more than 25 years. Most recently, he has been a regular contributor to BreakingModern.com, aNewDomain.net, and TechRepublic.